全文获取类型
收费全文 | 818篇 |
免费 | 18篇 |
国内免费 | 11篇 |
专业分类
化学 | 357篇 |
晶体学 | 5篇 |
力学 | 19篇 |
数学 | 342篇 |
物理学 | 124篇 |
出版年
2023年 | 8篇 |
2022年 | 21篇 |
2021年 | 45篇 |
2020年 | 11篇 |
2019年 | 14篇 |
2018年 | 21篇 |
2017年 | 19篇 |
2016年 | 44篇 |
2015年 | 21篇 |
2014年 | 29篇 |
2013年 | 76篇 |
2012年 | 61篇 |
2011年 | 55篇 |
2010年 | 44篇 |
2009年 | 30篇 |
2008年 | 55篇 |
2007年 | 44篇 |
2006年 | 32篇 |
2005年 | 40篇 |
2004年 | 29篇 |
2003年 | 14篇 |
2002年 | 16篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 13篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 11篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 3篇 |
1974年 | 1篇 |
排序方式: 共有847条查询结果,搜索用时 15 毫秒
91.
Gee MB Cox NR Jiao Y Bentenitis N Weeerasinghe S Smith PE 《Journal of chemical theory and computation》2011,7(5):1369-1380
A classical nonpolarizable force field is presented for the simulation of aqueous alkali halide solutions (MX), where M = Li(+), Na(+), K(+), Rb(+), Cs(+) and X = F(-), Cl(-), Br(-), I(-), and their interactions with biomolecules. The models are specifically designed to reproduce the experimental Kirkwood-Buff integrals, and thereby the solution salt activities, as a function of salt concentration. Additionally, we demonstrate that these models reasonably reproduce other experimental properties including ion diffusion constants, dielectric decrements, and the excess heats of mixing. The parameters are developed by considering the properties of aqueous NaX and MCl solutions using a previously established model for NaCl. Transferability of the parameters to other salts is then established by the successful simulation of additional aqueous salt solutions, KI and CsBr, not originally included in the parameterization procedure. 相似文献
92.
At the intersection of nonlinear and combinatorial optimization, quadratic programming has attracted significant interest
over the past several decades. A variety of relaxations for quadratically constrained quadratic programming (QCQP) can be
formulated as semidefinite programs (SDPs). The primary purpose of this paper is to present a systematic comparison of SDP
relaxations for QCQP. Using theoretical analysis, it is shown that the recently developed doubly nonnegative relaxation is
equivalent to the Shor relaxation, when the latter is enhanced with a partial first-order relaxation-linearization technique.
These two relaxations are shown to theoretically dominate six other SDP relaxations. A computational comparison reveals that
the two dominant relaxations require three orders of magnitude more computational time than the weaker relaxations, while
providing relaxation gaps averaging 3% as opposed to gaps of up to 19% for weaker relaxations, on 700 randomly generated problems
with up to 60 variables. An SDP relaxation derived from Lagrangian relaxation, after the addition of redundant nonlinear constraints
to the primal, achieves gaps averaging 13% in a few CPU seconds. 相似文献
93.
In this paper we present a new framework for identifying preferred solutions to multi-objective binary optimisation problems.
We develop the necessary theory which leads to new formulations that integrate the decision space with the space of criterion
weights. The advantage of this is that it allows for incorporating preferences directly within a unique binary optimisation
problem which identifies efficient solutions and associated weights simultaneously. We discuss how preferences can be incorporated
within the formulations and also describe how to accommodate the selection of weights when the identification of a unique
solution is required. Our results can be used for designing interactive procedures for the solution of multi-objective binary
optimisation problems. We describe one such procedure for the multi-objective multi-dimensional binary knapsack formulation
of the portfolio selection problem. 相似文献
94.
C-H(ax)···Y(ax) contacts are a textbook prototype of steric hindrance in organic chemistry. The nature of these contacts is investigated in this work. MP2/6-31+G(d,p) calculations predicted the presence of improper hydrogen bonded C-H(ax)···Y(ax) contacts of different strength in substituted cyclohexane rings. To support the theoretical predictions with experimental evidence, several synthetic 2-substituted adamantane analogues (1-24) with suitable improper H-bonded C-H(ax)···Y(ax) contacts of different strength were used as models of a substituted cyclohexane ring. The (1)H NMR signal separation, Δδ(γ-CH(2)), within the cyclohexane ring γ-CH(2)s is raised when the MP2/6-31+G(d,p) calculated parameters, reflecting the strength of the H-bonded C-H(ax)···Y(ax) contact, are increased. In molecules with enhanced improper H-bonded contacts C-H(ax)···Y(ax), like those having sterically crowded contacts (Y(ax) = t-Bu) or contacts including considerable electrostatic attractions (Y(ax) = O-C or O═C) the calculated DFT steric energies of the γ-axial hydrogens are considerably reduced reflecting their electron cloud compression. The results suggest that the proton H(ax) electron cloud compression, caused by the C-H(ax)···Y(ax) contacts, and the resulting increase in Δδ(γ-CH(2)) value can be effected not just from van der Waals spheres compression, but more generally from electrostatic attraction forces and van der Waals repulsion, both of which are improper H-bonding components. 相似文献
95.
Tsoureas N Kuo YY Haddow MF Owen GR 《Chemical communications (Cambridge, England)》2011,47(1):484-486
The addition of H(2) across a transition metal-borane bond is reported for the first time providing a mechanism for recharging borane functional groups to borohydride. 相似文献
96.
97.
DNA block copolymer doing it all: from selection to self-assembly of semiconducting carbon nanotubes
98.
Nikolaos Gialelis Ioannis G. Stratis 《Mathematical Methods in the Applied Sciences》2019,42(15):4939-4956
We show local existence of certain type of solutions for the Cauchy problem of the defocusing nonlinear Schrödinger equation with pure power nonlinearity, in various cases of open sets, unbounded or bounded. These solutions do not vanish at the boundary or at infinity. We also show, in certain cases, that these solutions are unique and global. 相似文献
99.
Polykarpos Porfyrakis Nikolaos L. Tsitsas Dimitri J. Frantzeskakis 《Mathematical Methods in the Applied Sciences》2019,42(18):7326-7334
A nonlinear (Kerr‐type) electromagnetic metamaterial, characterized by a double‐Lorentz model of its frequency‐dependent linear effective dielectric permittivity and magnetic permeability, is considered. The formation of gap solitons in the low‐ and high‐frequency band gaps of this metamaterial is investigated analytically. Evolution equations governing the gap solitons, of the form of a nonlinear Klein‐Gordon and a nonlinear Schrödinger equation, are obtained, and the structure of their solutions is discussed. 相似文献
100.
James N. Tsoporis Ioannis-Alexandros Drosatos Sahil Gupta Hajera Amatullah Shehla Izhar Claudia C. dos Santos Vasileos Salpeas Angelos G. Rigopoulos Ioannis K. Toumpoulis Andreas S. Triantafyllis Eleftharios Sakadakis Nikolaos Kavantzas John C. Marshall Ioannis K. Rizos Thomas G. Parker 《Molecules (Basel, Switzerland)》2021,26(13)
DJ-1 was originally identified as an oncogene product while mutations of the gene encoding DJ-1/PARK7 were later associated with a recessive form of Parkinson’s disease. Its ubiquitous expression and diversity of function suggest that DJ-1 is also involved in mechanisms outside the central nervous system. In the last decade, the contribution of DJ-1 to the protection from ischemia-reperfusion injury has been recognized and its involvement in the pathophysiology of cardiovascular disease is attracting increasing attention. This review describes the current and gaps in our knowledge of DJ-1, focusing on its role in regulating cardiovascular function. In parallel, we present original data showing an association between increased DJ-1 expression and antiapoptotic and anti-inflammatory markers following cardiac and vascular surgical procedures. Future studies should address DJ-1’s role as a plausible novel therapeutic target for cardiovascular disease. 相似文献